1. Field of the Invention
This invention relates to integrated circuit (IC) chips of the type having diffused therein a Zener diode junction to provide a reference voltage. More particularly, this invention relates to such a Zener diode formed with a special diffusion pattern to provide significantly improved characteristics, especially enhanced stability in operation.
2. Description of the Prior Art
IC devices have for some time now included Zener diode junctions to provide a reference voltage for the associated circuitry on the chip. Typically in such arrangements the breakdown occurs at the p.sup.+ N.sup.+ junction at the silicon/silicon dioxide interface of the chip. There have, however, been problems with such devices, especially drift of the breakdown voltage, e.g. as a function of time and with changes in temperature.
It has been suggested that the cause of such instability is related to the presence of the passivating/insulating layer of silicon dioxide which lies adjacent the silicon surface where breakdown takes place. It reportedly has been proposed to employ a device with subsurface breakdown based on the use of ion implantation, which theoretically could avoid problems encountered with the typical surface breakdown diodes. However, the ion implantation approach is not truly satisfactory, especially because the required manufacturing process becomes relatively complicated. Accordingly, there has been a need to provide an improved IC Zener diode whereby superior stability and other desirable characteristics can be achieved with a relatively simple manufacturing process.